Many butterflies are perfectly fine to feed. Some moths are not okay to feed. You just have to research a little. Cabbage whites, painted ladies, buckeyes, red admirals, west coast ladies, and american ladies (butterflies) are all safe to feed and very common. Some giant american silkmoths are not okay to feed and some of the caterpillars sting you!
I'll take your hornworms from your tomatoes and send you eggs!